1. Field of the Invention
The present invention relates to a postprocessing apparatus for performing a predetermined postprocessing to a recording sheet to which a predetermined processing is performed preliminarily in an upstream device such as an image forming apparatus and discharging the recording sheet, and an image forming system adopting the same.
2. Description of the Related Art
Conventionally, an apparatus for performing a postprocessing to a recording sheet as described in Japanese Patent Publication No. 2004-99274 has been known. The postprocessing apparatus receives a recording sheet to which an image forming processing is performed in an upstream device including an image forming apparatus, performs a postprocessing such as a punching processing and a stapling processing to the recording sheet and then discharges the recording sheet. The stapling processing of binding a plurality of received recording sheets with a binding needle is performed in a stapling unit which is detachably mounted in a main body (housing) of the apparatus.
The stapling unit includes a receiving side unit provided at a slant in the main body and a cover unit covered on an upper surface of the receiving side unit. A plurality of recording sheets are aligned and stored in a gap (processing space) between the units. Accordingly, a stack of recording sheet is formed. A stapler is integrally provided between the units, and the stapling processing is performed to the stack of recording sheets by a predetermined operation of the stapler. The stack of recording sheets after the stapling processing performed thereto is completed is discharged from the processing space between the units to an outer portion.
To position the recording sheets led into the processing space at a predetermined position and discharge the stack of recording sheets after the stapling processing thereto is completed, the receiving side unit is provided with an endless belt which is positioned so as to surround the receiving side unit and revolves around the rollers provided in upper and lower portions of the receiving side unit. Further, a sheet receiving member for receiving the recording sheet on the endless belt and supporting the same is provided projectingly. Then, the stack of recording sheets formed in the processing space is conveyed or positioned at a determined position in the processing space by the sheet receiving member moved or stopped in accordance with a revolving of the endless belt.
In a lower portion of the stapling unit in the main body, a center-folding unit is provided. The center-folding unit is a unit for bending the stack of recording sheets to which the stapling processing is performed at a central portion in a longitudinal direction of the recording sheet such that the stapled recording sheets bend along a position at which the stapling processing is performed. Namely, the center-folding unit is a unit for performing a bending processing. The center-folding unit performs the bending processing to the stack of recording sheets by pressing the stapled position of the stack of recording sheets toward a nipping portion of a pair of center-folding rollers with a plate-like pressing member.
On the side of the center-folding unit at a boundary position between the stapling unit and the center-folding unit, a pair of conveying rollers for conveying the stack of recording sheets which is to be bent after the stapling processing to the bending position of the center-folding unit is provided. The stack of recording sheets which is to be bent is conveyed smoothly from the stapling unit to the bending position of the center-folding unit by a driving of the pair of conveying rollers. The stack of recording sheets after the center-folding processing is performed pass through the pair of center-folding rollers and is discharged to a discharging tray exclusively used for the center-folding processing.
In the postprocessing apparatus described in the patent document, the stapler is provided in the stapling unit which is so constructed as to be detachable with respect to the main body. However, if the stapler, which is such a heavy-load item having a complex structure, is provided on the side of the stapling unit, the stapling unit may become heavier and have a complex structure, or may become so heavy that attaching and detaching operation of the stapling unit involves a difficulty.
To resolve such disadvantages, a stapler-separation type postprocessing apparatus has been recently proposed and practically used. In the stapler-separation type postprocessing apparatus, the stapler is mounted in the side of the main body of the apparatus. The stack of recording sheets are aligned in the processing space in the stapling unit and conveyed to the stapler by a movement of the sheet receiving member with a revolving of the endless belt. Then, the stapling processing is performed to the stack of recording sheets.
In the stapler-separation type postprocessing apparatus, the stapler is provided in a lower end portion of the stapling unit. Therefore, it is necessary to provide an alternative route which detours the stapler for conveyance of the recording sheet to which the center-folding processing is performed in the stapling unit to the center-folding unit. Since the alternative route is liable to have such a long length, it is necessary to provide a conveyer also in the alternative route for conveying the stack of recording sheets to the center-folding unit.
Meanwhile, it is less often to perform the center-folding processing to the stack of recording sheets in the postprocessing apparatus, and many users do not require the center-folding unit. On the other hand, there exist users who need the center-folding unit. To meet the contradicting needs of users, it can be considered to construct the postprocessing apparatus to have a fundamental structure including only the stapling unit, and the center-folding unit may be selectively mounted in accordance with needs of users.
In the postprocessing apparatus which is so constructed that the center-folding unit is selectively mountable to the one having a fundamental structure of the stapler separation type, the conveyer for conveying the stack of recording sheets to the center-folding unit is provided in the alternative route to detour the stapler as described above. If the postprocessing unit is so constructed that a driving force is transmitted from a driver mounted on the side of the stapling unit to the conveyer through a driving force transmission mechanism, a problem arises in which the cost is caused to increase even when the center-folding unit is not mounted in the postprocessing apparatus. Meanwhile, since the center-folding unit is integrally mounted in the main body by default in the postprocessing apparatus disclosed in the Japanese patent Publication No. 2004-99274, it is not susceptible to cause such problem as described above.